Alkali-resistant glass compositions

ABSTRACT

Glass compositions with a particularly high alkali resistance comprise, in weight percentages: 
     
         ______________________________________                                    
 
    
     SiO 2        45 to 65%                                                 
ZrO 2         6 to 20%                                                 
RO              20 to 45%                                                 
______________________________________                                    
 
     The total of SiO 2  + ZrO 2  + RO being not less than 94% by weight of the glass, where RO represents CaO, in an amount from 20 to 45%, with or without lesser amounts of further divalent oxides of the group consisting of MgO, SrO, BaO and ZnO, the balance (if any) of the composition consisting of compatible constituents such as TiO 2 , Al 2  O 3 , B 2  O 3 , Fe 2  O 3 , F 2  and R 2  O, where R 2  O represents K 2  O, Na 2  O or Li 2  O, the amount of any one of these compatible constituents not exceeding 5% by weight. Preferably R 2  O does not exceed 3%.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of application Ser. No. 426,142 filed Dec. 19, 1973 (now abandoned).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to alkali-resistant glass compositions and particularly, though not exclusively, to such compositions which can be formed into glass fibres.

2. Description of the Prior Art

It is known to include a proportion of zirconia (ZrO₂) in glass compositions for enhancing their resistance to alkalis. It is also known that the inclusion of substantial proportions of boron oxide (B₂ O₃) and/or alkali metal oxides (R₂ O) has a deleterious effect on the alkali resistance of the glass, although both these constituents have other favourable properties which have hitherto been considered to make their inclusion desirable. For example, both B₂ O₃ and R₂ O act as fluxes to aid melting and thus help to overcome the tendency of ZrO₂ to make melting difficult, and they can also improve the characteristics of the glass for drawing glass fibres.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide glass compositions with a particularly high alkali resistance.

According to the present invention, the major components of the glass composition comprise, in weight percentages:-

    ______________________________________                                         SiO.sub.2       45 to 65%                                                      ZrO.sub.2        6 to 20%                                                      RO              20 to 45%                                                      ______________________________________                                    

The total of SiO₂ + ZrO₂ + RO being not less than 94% by weight of the glass, where RO represents at least one divalent oxide of the group consisting of CaO, MgO, SrO, BaO and ZnO, the amount of said divalent oxide or oxides lying within the ranges, in weight percentages: CaO 20 to 45%; MgO 0 to 10%; SrO 0 to 8%; BaO 0 to 10% and ZnO 0 to 5%.

The balance of the composition may consist of at least one of the following constituents: TiO₂, Al₂ O₃, B₂ O₃, Fe₂ O₃, F₂ and R₂ O, where R₂ O represents K₂ O, Na₂ O, or Li₂ O, the amount of any one of the said constituents not exceeding 5% by weight of the composition. Preferably the amount of R₂ O does not exceed 3% by weight of the composition.

The glass compositions according to the invention thus contain relatively large proportions of ZrO₂, while being free from, or containing only low proportions of, B₂ O₃ and R₂ O. In spite of the absence or low level of these fluxing agents, it has proved possible to melt the glass compositions quite readily.

When subjected to standard tests for chemical durability in aqueous and in alkaline environments, such glass compositions have shown excellent results. It has also proved possible to form them into glass wool fibres, e.g. by high temperature blown type processes.

DETAILED DESCRIPTION OF THE INVENTION

Specific embodiments of glass compositions in accordance with the invention will now be described by way of example.

The following Table 1 lists 18 glass compositions consisting of ZrO₂, SiO₂ and CaO, illustrating the use of four different values for ZrO₂ (18, 14, 10 and 8 weight %) with varying proportions of SiO₂ between 45 and 65 weight % and correspondingly inversely varying proportions of CaO between 45 and 21 weight %.

                  TABLE 1                                                          ______________________________________                                         wt.%         wt.%          wt.%                                                ZrO.sub.2    SiO.sub.2     CaO                                                 ______________________________________                                         18           45            37                                                  18           50            32                                                  18           55            27                                                  18           60            22                                                  14           45            41                                                  14           50            36                                                  14           55            31                                                  14           60            26                                                  14           65            21                                                  10           45            45                                                  10           50            40                                                  10           55            35                                                  10           60            30                                                  10           65            25                                                  8            48            44                                                  8            50            42                                                  8            55            37                                                  8            60            32                                                  ______________________________________                                    

Table 2 lists 24 further glass compositions, each of which is identified by a number C/07 followed by a three-figure number. For most of the glasses in Table 2, the composition is given both in mole percentages and in weight percentages and the liquidus temperature and the results of standard chemical durability tests are given. In the latter tests, 10 gm samples of the glass are ground to a powder and treated with 50 c.c. of the specified reagent (water, N/10 NaOH and N.NaOH respectively). The weights of the component oxides extracted (in milligrams) are listed in Table 2.

                                      TABLE 2                                      __________________________________________________________________________               157     158    159    163                                            Glass No. C/07                                                                           Mol                                                                               Wt.% Mol                                                                               Wt.%                                                                               Mol                                                                               Wt.%                                                                               Mol                                                                               Wt.%                                        __________________________________________________________________________      SiO.sub.2                                                                               54 51.55                                                                               58 55.2                                                                               55 53.6                                                                               50 47.9                                         ZrO.sub.2                                                                               7  13.7 7  13.7                                                                               5  10.0                                                                               7  13.7                                        CaO       39 34.75                                                                               35 31.1                                                                               40 36.4                                                                               43 38.4                                        MgO                                                                            SrO                                                                            BaO                                                                             TiO.sub.2                                                                      Na.sub.2 O                                                                    ZnO                                                                            Liquidus  1405    1420   1450   450                                            Temperature T.sub.L ° C.                                                Chemical Durability                                                                 Oxide                                                                     Reagent                                                                             extracted                                                                      Na.sub.2 O                                                                H.sub.2 O                                                                           SiO.sub.2                                                                           1.0     1.0    0.6    1.2                                                 CaO  0.63    0.65   1.1    0.73                                           N/10 SiO.sub.2                                                                           0.6     0.8    1.6    1.05                                           NaOH CaO  0.26    0.26   0.24   0.31                                           N    SiO.sub.2                                                                           1.4     1.25   1.2    1.25                                           NaOH CaO  0.59    0.74   0.81   0.75                                           __________________________________________________________________________               171     174    178                                                   Glass No.C/07                                                                            Mol                                                                               Wt%  Mol                                                                               Wt.%                                                                               Mol                                                                               Wt.%                                               __________________________________________________________________________      SiO.sub.2                                                                               60 57.44                                                                               54 52.2                                                                               58 55.9                                                ZrO.sub.2                                                                               7  13.74                                                                               7  13.9                                                                               7  13.8                                               CaO       29 25.91                                                                               34 30.7                                                                               30 27.0                                               MgO       3  1.92 5   3.2                                                                               5   3.2                                               SrO                                                                            BaO                                                                             TiO.sub.2                                                                      Na.sub.2 O                                                                              1  0.99                                                              ZnO                                                                            Liquidus  1420    1415   1410                                                  Temperature T.sub.L ° C                                                 Chemical Durability                                                                 Oxide                                                                     Reagent                                                                             extracted                                                                      Na.sub.2 O                                                                          0.22                                                                      SiO.sub.2                                                                           0.6     0.4    0.3                                                   H.sub.2 O                                                                           CaO  0.41    0.47   0.29                                                  N/10 SiO.sub.2                                                                           1.6     0.6    1.3                                                   NaOH CaO  0.16    0.52   0.1                                                   N    SiO.sub.2                                                                           2.0     0.65   1.2                                                   NaOH CaO  0.5     2.0    0.26                                                  __________________________________________________________________________               179     183    186    199                                            Glass No.C/07                                                                            Mol                                                                               Wt.% Mol                                                                               Wt.%                                                                               Mol                                                                               Wt.%                                                                               Mol                                                                               Wt.%                                        __________________________________________________________________________      SiO.sub.2                                                                               56 53.7 58 55.0   58.2                                                                               54 51.4                                         ZrO.sub.2                                                                               7  13.75                                                                               7  13.63  14.0                                                                               7  13.66                                       CaO       30 26.8 28 24.8   22.8                                                                               32 28.44                                       MgO       5  3.2  5  3.2        5  3.19                                        SrO               2  3.3        2  3.28                                        BaO                                                                             TiO.sub.2                                                                               2  2.55                                                               Na.sub.2 O                  5.0                                               ZnO                                                                            Liquidus                                                                       Temperature T.sub.L ° C                                                           1395    1418   1370   1400                                           Chemical Durability                                                                 Oxide                                                                     Reagent                                                                             extracted                                                                      Na.sub.2 O          0.33                                                  H.sub.2 O                                                                           SiO.sub.2    0.25   0.8    1.0                                                 CaO  1.02    0.35   0.42   0.37                                           N/10 SiO.sub.2                                                                           1.15    0.85   1.2    0.8                                            NaOH CaO  0.25    0.1    0.21   0.2                                            N    SiO.sub.2                                                                           1.3            2.0    0.4                                            NaOH CaO  0.95    0.25   0.5    0.25                                           __________________________________________________________________________               201     202    204    205                                            Glass No.C/07                                                                            Mol                                                                               Wt.% Mol                                                                               Wt.%                                                                               Mol                                                                               Wt.%                                                                               Mol                                                                               Wt.%                                        __________________________________________________________________________      SiO.sub.2                                                                               54 50.66                                                                               54 52.1                                                                               56 52.93                                                                              58 54.23                                        ZrO.sub.2                                                                               7  13.46                                                                               7   13.85                                                                             9  17.44                                                                              7  13.41                                       CaO       30 26.27                                                                               32 28.8                                                                               30 26.47                                                                              28 24.44                                       MgO       5  3.14 5   3.2                                                                               5   3.17                                                                              5  3.14                                        SrO       4  6.47                                                              BaO                             2  4.77                                         TiO.sub.2                                                                      Na.sub.2 O       2  1.99                                                      ZnO                                                                            Liquidus                                                                       Temperature T.sub.L ° C                                                           1400    1365   1450   1405                                           Chemical Durability                                                                 Oxide                                                                     Reagent                                                                             extracted                                                                      Na.sub.2 O   0.46                                                              SiO.sub.2                                                                              0.3  0.6    0.5    0.3                                                 CaO     0.7  0.37   0.26   0.2                                            H.sub.2 O    0.06                                                                           SrO                                                                    BaO                        0.25                                                SiO.sub.2                                                                              1.3  1.3    1.0    0.95                                           N/10                                                                                CaO     0.1  0.12   0.39   0.3                                                 MgO                        0.05                                           NaOH                                                                                BaO                        0.25                                                SiO.sub.2                                                                              1.5  2.7    1.8    1.3                                                 CaO     0.43 0.49   0.44   0.2                                            NaOH      0.1                                                                               SrO                                                                    MgO                 0.1    0.05                                                BaO                        0.25                                           __________________________________________________________________________               206     208    209    211                                            Glass No.C/07                                                                            Mol                                                                               Wt.% Mol                                                                               Wt.%                                                                               Mol                                                                               Wt.%                                                                               Mol                                                                               Wt.%                                        __________________________________________________________________________      SiO.sub.2                                                                               58 58.48   65.0   65.0   52.0                                         ZrO.sub.2                                                                               7  13.73   10.0   12.0   18.0                                        CaO       28 25.0    20.0   20.0   29.0                                        MgO       5  3.21                                                              SrO                                                                            BaO                                                                             TiO.sub.2                                                                      Na.sub.2 O           5.0    3.0   1.0                                         ZnO       2  2.59                                                              Liquidus                                                                       Temperature T.sub.L ° C                                                           1410                                                                 Chemical Durability                                                                 Oxide                                                                     Reagent                                                                             extracted                                                                      Na.sub.2 O   0.22   0.135                                                      SiO.sub.2                                                                           0.4     0.7    0.25                                                  H.sub.2 O                                                                           CaO  0.2     0.19   0.135                                                      BaO                                                                            ZnO  0.5                                                                       SiO.sub.2                                                                           0.5     1.15   1.05                                                  N/10 CaO  0.15    0.1    0.1                                                        MgO                                                                       NaOH                                                                                BaO                                                                            ZnO  0.1                                                                       SiO.sub.2                                                                           2.85    2.25   2.25                                                  N    CaO  0.3     0.28   0.25                                                       MgO                                                                       NaOH                                                                                BaO                                                                            ZnO  0.15                                                                 __________________________________________________________________________               212     213    214    215    216                                     Glass No.C/07                                                                            Mol                                                                               Wt.% Mol                                                                               Wt.%                                                                               Mol                                                                               Wt.%                                                                               Mol                                                                               Wt.%                                                                               Mol                                                                               Wt.%                                 __________________________________________________________________________      SiO.sub.2   51.0    50.0   52.0   54.0   55.0                                  ZrO.sub.2   19.0    20.0   14.0   13.5   6.0                                  CaO          29.0    29.0   24.0   21.5   39.0                                 MgO                         10.0   3.0                                         SrO                                                                            BaO                                8.0                                          TiO.sub.2                                                                      Na.sub.2 O  1.0      1.0                                                      ZnO                                                                            Liquidus                                                                       Temperature T.sub.L ° C                                                 Chemical Durability                                                                 Oxide                                                                     Reagent                                                                             extracted                                                                      Na.sub.2 O                                                                          0.13                                                                      SiO.sub.2                                                                           0.4            0.25   0.35   1.6                                     H.sub.2 O                                                                           CaO  0.225          0.14   0.15   0.9                                          BaO                                                                            ZnO                                                                            SiO.sub.2                                                                           0.7            0.65   0.85   0.9                                     N/10                                                                                CaO  0.13           0.12   0.15   0.15                                    NaOH                                                                                MgO                                                                            BaO                        0.05                                                ZnO                                                                            SiO.sub.2                                                                           1.65           1.55   1.9    2.6                                          CaO  0.35           0.34   0.3    0.6                                          MgO                                                                       NaOH                                                                                BaO                        0.1                                                 ZnO                                                                       __________________________________________________________________________

The liquidus temperatures of glasses C/07/208 to 216 inclusive were not precisely measured, but it was ascertained that they all fell within the range from 1400° C. to 1500° C. The chemical durability of glasses C/07/211 and 213 was not measured because these glasses are very similar to glass 212, differing only in the content of ZrO₂ with consequential adjustment to the SiO₂ content, and they can consequently be confidently predicted to have similar chemical durability, 211 being slightly less good due to its lower ZrO₂ and 213 being slightly better due to its higher ZrO₂ content.

When using the maximum permissible amount of SiO₂ (65 weight %) a proportion of up to 5 weight % Na₂ O may be included, as in glasses C/07/208 and 209, to improve the drawing characteristics of the glass and thereby facilitate the formation of fibres. These glasses also contain the minimum permissible amount of RO (20 weight%) in the form of CaO. In general, the amount of RO increases as the amount of SiO₂ is reduced. As shown by the foregoing Examples, CaO may vary between 20 and 45%, and up to 10% of the RO may consist of MgO, as in glass C/07/214. Up to 10% of the RO can be BaO, up to 8% of the RO can be SrO, and up to 5% of the RO can be ZnO, if desired. With MgO or SrO present, a slight lowering of the liquidus temperature can be achieved, which is beneficial for formation of glass fibres. A small amount of TiO₂ can also be included, as in glass C/07/179, to produce a similar lowering of the liquidus temperature, but TiO₂ also tends to reduce the alkali resistance so it can only be used to a limited extent, i.e. up to 5 weight %. Al₂ O₃ produces similar effects.

B₂ O₃ or F₂ could also be included in amounts of up to 5 weight % to assist melting. Fe₂ O₃ may be present in the customary small amounts (up to 0.5 weight %) which result from the normal impurities in raw materials. 

We claim:
 1. An alkali-resistant glass composition consisting essentially of, in weight percentages:

    ______________________________________                                         SiO.sub.2       45 to 65%                                                      ZrO.sub.2        6 to 20%                                                      RO              20 to 45%                                                      ______________________________________                                    

the total of SiO₂ + ZrO₂ + RO being not less than 94% by weight of the glass, where RO represents at least one divalent oxide of the group consisting of CaO, MgO, SrO, BaO and ZnO, the amount of said divalent oxide or oxides lying within the ranges, in weight percentages: CaO 20 to 45%, MgO 0 to 10%; SrO 0 to 8%; BaO 0 to 10% and ZnO 0 to 5% and wherein if components other than SiO₂, ZrO₂ and RO are included in said glass composition, each such component does not exceed 5% by weight of the composition.
 2. A glass composition according to claim 1, wherein said glass composition includes at least one component selected from the group of TiO₂, Al₂ O₃, B₂ O₃, Fe₂ O₃, F₂ and R₂ O, where R₂ O represents K₂ O, Na₂ O or Li₂ O.
 3. A glass composition according to claim 2, wherein the amount of R₂ O does not exceed 3% by weight of said composition.
 4. A glass composition according to claim 2, wherein SiO₂ = 65% and CaO = 20% and said composition also contains 5% Na₂ O by weight.
 5. An alkali-resistant glass composition consisting essentially of, in weight percentages:

    ______________________________________                                         SiO.sub.2                                                                               +5          to         65%                                            ZrO.sub.2                                                                               6           to         20%                                            RO       20          to         45%                                            TiO.sub.2                                                                               0           to         5%                                             Al.sub.2 O.sub.3                                                                        0           to         5%                                             B.sub.2 O.sub.3                                                                         0           to         5%                                             Fe.sub.2 O.sub.3                                                                        0           to         5%                                             F.sub.2  0           to         5%                                             ______________________________________                                    

R₂ O (K₂ O, Na₂ O or Li₂ O) 0 to 5% the total of SiO₂ + ZrO₂ + RO being from 94% to 100% by weight of the glass, where RO represents the total of one or more divalent oxides of the group consisting of CaO, MgO, SrO, BaO and ZnO, the amount of said divalent oxide or oxides lying within the ranges, in weight percentages:

    ______________________________________                                         CaO      20          to         45%                                            MgO      0           to         10%                                            SrO      0           to         8%                                             BaO      0           to         10%                                            ZnO      0           to         5%                                             ______________________________________                                     